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What Tire Size?

This is a discussion on What Tire Size? within the Wheels and Tires forums, part of the General Help category; I have found a killer deal on some rims and am looking for some tires, question is what would be ...

  1. #1
    LS1-TA schrysler's Avatar
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    1998 Trans Am Vert

    What Tire Size?

    I have found a killer deal on some rims and am looking for some tires, question is what would be the best tire sizes for 18x9.5 in back and 18x8.5 in the front? The back is a no brainer for me either 275/35/18 or 295/35/18 but the front is where i am getting stuck, why do people do 245/40/18 in the front instead of keeping it 35?
    1998 Trans Am Vert, M6, Soon to be full of goodies......

  2. #2
    2 SS's are better than 1 Jays00ss's Avatar
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    NBM / Silver
    00 SS / 71 SS Elcamino

    it stays true to the stock diameter.

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    LS1-TA schrysler's Avatar
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    BUT THE FRONT AND THE BACK ARE 18's isnt the 35 or 40 the amount of side wall? I would think that it would look weird having two different size sidewalls on the same car.

  4. #4
    Senior Member mrr23's Avatar
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    dark bowling green
    2000 corvette

    Quote Originally Posted by schrysler View Post
    BUT THE FRONT AND THE BACK ARE 18's isnt the 35 or 40 the amount of side wall? I would think that it would look weird having two different size sidewalls on the same car.
    sidewall height is determined by width. that 40 is a percentage number. 40% of 245mm gives you the sidewall height.

    i give tire sizes that are equivalent to factory tire diameter in the sticky above.

    tire size equivalents

    the 245/40-18 and the 275/35-18 have the same amount of sidewall. both on 18" wheels and both are 25.7" tall.

  5. #5
    Junior Member Talenuf's Avatar
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    1997 Trans Am WS6 vert

    Somewhere here is a chart of acceptable tire sizes for given wheel widths. Can somebody drop the link to that here? Thanks!

  6. #6
    Crazy Canuck ! Eugenio_SS's Avatar
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    triple-black
    2000 CamaroSS convertible

    to calculate overall diameter... it's as follows:
    let's understand the #s.
    example : 275/40-17

    means
    275: width of tire = 275mm
    40: sidewall is 40% of 275mm = 275 x 0.40 = 110mm = 4.33" (note: 1" = 25.4mm)
    17: size of wheel = 17"

    Overall diameter = size of wheel + 2 sidewalls (the top and the bottom)
    OD = 17" + 2x4.33" = 25.66"

    so if we take 245/40-18
    sidewall: 245x0.4 = 98mm = 3.86"
    OD: 18" + 2x3.86" = 25.72"

    275/35-18
    sidewall: 275x0.35 = 96.25mm = 3.79"
    OD: 18" + 2x3.79" = 25.58"

    Hope this helps.
    Eugenio_SS
    almost stock triple-black 2000 SS convertible with 17x11s on all 4 w/ 315s at the track or on the street with 18x10.5s on all 4 w/ 315s: (1), (2)

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